This invention relates generally to supplemental restraint systems for use in motor vehicles and, more particularly, to supplemental inflatable restraint systems which are housed within a vehicle interior trim product behind or below an opening which is closed by a door that opens in response to air bag inflation.
Supplemental inflatable restraint systems (SIRSs) require a cover that opens to provide a path through which an air bag may deploy into the passenger compartment as the air bag inflates.
Some of the prior art SIRS covers include air bag doors with hinges that allow the doors to swing open in response to air bag inflation. These doors may be mid-mounted on the front vertical face of an instrument panel as shown in U.S. Pat. No. 3,708,179 or may be mounted on an upper surface of an instrument panel or dash board as shown in U.S. Pat. Nos. 4,946,653 and 4,893,833.
One problem with such prior art systems is that the air bag door edges are positioned where children can pry the door open unless it is firmly fastened in place by interlocking mechanical members. Moreover, even if members are designed to interlock securely enough to preclude occupants from prying the air bag door open, such interlocking members may not predictably release the air bag door promptly enough in response to air bag inflation. In such cases, the door may not fully open and may, as a result, obstruct the air bag as it deploys into the vehicle passenger compartment.
One solution to such problems is set forth in U.S. Pat. No. 5,066,037 in which a flange on the door closure is fit within a U-shaped clamp. In such arrangements the locking flange and clamp must be separately positioned and aligned during the assembly of the supplemental inflatable restraint system.
xe2x80x9cAnother solution is disclosed in U. S. Pat. No. 5,458,365 in which slotted cylindrical heads on specially-molded probes 26 snap into cylindrical sockets 24 in base members 22 to hold an air bag door closed, but yield and pop out of the sockets when the air bag is deployed. Both the probes 26 and the base members 22 must be specially fabricated by injection molding or similar means.xe2x80x9d
Another solution, shown in FIGS. 8-15 of U.S. Pat. No. 5,150,919 involves pins 142 fabricated with threaded portions for attachment to threaded door-mounted studs 141. An enlarged head of each of the pins 142 extends through one of apertures 133a in an instrument panel support structure or canister flange. A spring pin 143 may be provided to hold the head of each pin 142 in its respective aperture 133a. Upon deployment, the pins 142 pop out of the holes 133a. 
Still another solution is set forth in U.S. Pat. No. 5,451,074 which is assigned to the assignee of the present invention. This patent shows a hold-down cable secured at its lower end to an instrument panel structure and provided at its upper end with an enlarged head, which is fitted into a keyhole slot 38 in an air bag door. In the embodiment of FIGS. 2-5 the cable and head are metal and, upon deployment, cause the slot portion 38b to deform to release the head 50. In the embodiments of FIGS. 6-9, the cable 92 and its head 134 are plastic and designed to deform upon air bag deployment. In each case, the heads and keyhole slots must be specially fabricated.
Each of the above solutions involves the manufacture and assembly of fasteners and support structures, or the formation of specially shaped sockets and receptacles. None of the above solutions can be implemented without fabricating fasteners and other such structures that do not exist in present systems and that would be time-consuming and expensive to engineer.
What is needed is a supplemental inflatable restraint system with a door hold-down assembly that can be manufactured and assembled without the expense of designing and fabricating new parts.
In accordance with this invention an inflatable restraint deployment system is provided comprising a simplified hold-down assembly that uses simple, commonly available or easily formable fasteners such as rivets and studs to releasably fasten an air bag door in a tamper-proof closed position. The deployment system comprises a hinged air bag door pivotally supported adjacent an air bag deployment opening in an air bag container. The air bag door is pivotally moveable about a hinged edge between a closed tamper-proof position covering the air bag deployment opening and an open, air bag-release position exposing the air bag deployment opening. A door hold-down member is supported in a fixed position adjacent the air bag deployment opening. A fastener hole rim defines a fastener hole in at least one of the air bag door and the door hold-down member. A door hold-down fastener releasably connects the air bag door to the hold-down member. The fastener includes an elongated shaft portion that extends from either the hold-down member or the air bag door through the fastener hole and is aligned with the direction the door would initially move if forced out of the closed position. A first fastener flange extends outward from around the fastener shaft portion. The first fastener flange engages the fastener hole rim to hold the air bag door in the closed position. The fastener has a first fastener cross-sectional area defined by the intersection of the door fastener and a plane extending perpendicular to the shaft portion through the first fastener flange. The fastener hole defines an area smaller than the first fastener cross-sectional area. Because of this, at least one of the fastener hole rim and the first fastener flange must yield when air bag inflation forces the door to pivot out of the closed position. This forced opening either pulls the door loose from the fastener and door hold-down member or pulls the door loose while retaining the fastener from the door hold-down member.
According to one aspect of the present invention, the door hold-down fastener comprises a stud-type fastener integrally extending from the air bag door. The stud-type fastener may be formed with a substrate portion of the air bag door as a single unitary piece.
According to another aspect of the present invention, the door fastener is a stud-type fastener that integrally extends from the door hold-down member. The stud-type fastener may be formed with the hold-down member as a single unitary piece.
According to another aspect of the present invention, the door fastener is a stud-type fastener that integrally extends from the air bag door. The stud-type fastener may be formed with the air bag door or a substrate portion of the air bag door as a single unitary piece.
According to another aspect of the present invention, the first fastener flange is a yielding stud head made of a yielding material such as plastic and the air bag door substrate is made of a non-yielding material such as metal. The first fastener flange may also be non-yielding, requiring that the fastener hole rim be formed in such a way that it will yield to the passage of the non-yielding fastener flange.
According to another aspect of the present invention, the door fastener is a rivet-type fastener and the fastener hole is the first of two fastener holes. The first fastener hole is disposed in said air bag door and the second fastener hole is disposed in the hold-down member. The first and second fastener holes are axially aligned when the air bag door is in the closed position. The rivet shaft portion extends through the first and second fastener holes and the rivet-type fastener includes a second rivet flange in the form of a rivet head that extends outwardly from the shaft portion adjacent the fastener base. The first and second fastener holes are disposed between said first and second fastener flanges. The rivet head engages the rim of one of the first and second fastener holes while the first fastener flange engages the rim of the other of the first and second fastener holes. The rivet may be any one of a number of commercially available rivets, either metal or plastic.
The invention additionally includes a method for releasably securing an air bag door in an inflatable restraint deployment system using a stud-type fastener. According to this method a base end of the elongated shaft portion of the stud-type fastener is connected to one of the hold-down member and the air bag door. When the air bag door is in the closed position the elongated shaft portion extends from the hold-down member parallel to the direction of door opening and is axially aligned with one of the first and second fastener holes. The stud-type fastener may be formed with either the hold-down member or the air bag door substrate as a single unitary piece. During final assembly, the air bag door is pivoted towards its closed position until the fastener hole contacts the stud flange. As the door continues towards its closed position the stud flange is forced to yield and deform as the fastener hole is forced over (or the fastener is forced through). As the door reaches its closed position the fastener hole passes completely over the stud flange allowing the stud flange to return to its approximate pre-deformation configuration. The stud may, alternatively, be formed initially as a hollow or solid cylinder that is heat staked to form the stud flange after the stud is passed through the fastener hole.
The invention additionally includes a method for releasably securing an air bag door in an inflatable restraint deployment system using a rivet-type fastener. According to this method the rivet-type fastener is installed in the hold-down member by moving the air bag door to its closed position and passing the elongated shaft portion through the first and second fastener holes. The rivet is then axially compressed to form the rivet flange at the end of the elongated portion of the rivet opposite the rivet head. The rivet head and rivet flange hold the door substrate and hold-down member together, securing the air bag door in its closed position.